1. Technical Field
The disclosure relates to an image processing method and an image processing device for a Gray output signal.
2. Related Art
An inkjet printer capable of color printing generally uses ink of four colors of cyan (C), magenta (M), yellow (Y), and black (K).
Meanwhile, there is known an inkjet printer further using a gray (Gray) ink to improve the color stability of gray and the density of dark portions in a printed image. In this inkjet printer, the color stability of gray and the density of dark portions can be improved by performing operations (1) and (2) described below.
(1) The CMY inks forming gray are replaced by a gray ink by using the concept of under color removal (UCR). Here, UCR is a publicly-known method of replacing the CMY inks with the K ink as disclosed in Japanese Unexamined Patent Application Publication No. 2015-142238 and the Specification of U.S. Pat. No. 4,812,899.
(2) The gray ink is added to pixels in each of which the K ink is ejected by an amount greater than a predetermined amount.
The operation (1) described above can prevent coloring of gray due to errors in ejection amounts and deviation of landing positions of the CMY inks. Hence, the color stability of gray is improved.
The operation (2) described above can improve the density of dark portions by causing the gray ink to be ejected in addition to the K ink.